The present invention relates in general to pressure sensitive adhesive tapes and more particularly to automotive harness tapes which in the course of normal driving are subjected to elevated temperatures of on the order of 135.degree. C. or greater.
The invention is an improvement over Applicant's U.S. Pat. No. 4,992,331 filed Sep. 30, 1988 and assigned to the present assignee. The prior application is hereby incorporated by reference. As stated therein it is highly desirable for such industrial adhesive tapes to possess characteristics such as impermeability to liquid, chemical resistance, flame retardancy, non-corrosion, tearability in the cross direction and conformability. Conformability is particularly desirable for application to automotive harness tapes which require tight wrapping around small objects. In accordance with the teachings of the aforementioned application, the backing layer comprises a chlorinated polyethylene.
While the presently available industrial tapes possess the aforementioned advantages, they do have disadvantages, one important disadvantage of which is lack of high temperature resistance. Commercially available tapes have optimal high temperature resistance in the range of 105.degree. C. Thus they do not resist temperatures of greater than 105.degree. C. for extended periods of time. Moreover, generally speaking, commercially available industrial tapes which are conformable are not high temperature resistant and high temperature resistant tapes are not conformable. (Conformability is subjectively defined by the capacity to wrap small objects, and is objectively defined by the American Society for Testing and Materials (ASTM) 1388 Cantilever method.) Thus high temperature resistance and conformability are considered to be mutually exclusive characteristics in the prior art. Yet the need exists in the industry and particularly the automotive industry for harness tapes which are both conformable high temperature resistant. This need is particularly felt in the automotive industry wherein the harness wraps are subjected to high temperatures during the operation of the engine. The backing of prior art tapes which are conformable, disintegrates at high temperatures, whereas the backing in prior art high temperature resistant tapes disassociates from the adhesive. Likewise, the adhesive may become less viscous at high temperatures which severely decreases the adhesive joint strength.
Accordingly, the primary objective of the present invention is to fulfill the longfelt need for a conformable high temperature resistant pressure sensitive adhesive tape which maintains the structural and functional integrity of both its backing and adhesive layer at high temperatures ranging beyond 135.degree. C.